1. Field of the Invention
This invention relates to a fire-retardant, or flame-retardant, polyamide composition having good heat resistance. More specifically, it relates to a fire-retardant polyamide composition having markedly improved thermal stability during molding.
2. Description of the Prior Art
Polyamides typified by 6 nylon and 66 nylon have excellent mechanical strength, rigidity, heat resistance and oil resistance, and by utilizing these properties, attempts have been made to exploit their applications as engineering plastics in some machine parts, electrical appliance parts and automobile parts. To improve their heat resistance and rigidity further, compositions of polyamides and glass fibers have also been used.
Polyamides composed of aromatic dicarboxylic acids such as terephthalic acid and aliphatic alkylenediamines (Japanese Laid-Open Patent Publication No. 53536/1984) or polyamides composed of aromatic diamines such as xylylenediamine and aliphatic dicarboxylic acids (Japanese Laid-Open Patent Publication No. 200420/1982) are known as polyamides having improved mechanical strength, rigidity and heat resistance over 6 nylon and the like.
Since polyamides, like other thermoplastic resins such as polyolefins, are liable to catch fire and burn, the addition of a fire retardant is required when the polyamides are to be used in fields requiring self-extinguishing property and flame retardancy. A composition of a polyamide and a halogenated polystyrene (Japanese Laid-Open Patent Publication No. 47034/1976) and a composition of a polyamide and a condensation product of brominated phenol (Japanese Patent Publication No. 2100/1981) have been proposed for such fire-retarding purposes. These patent documents disclose that glass fibers as a reinforcing agent and antimony trioxide as a fire-retarding aid may further be incorporated.
However, since polyamides, especially polyamides having excellent heat resistance, are generally compounded at high temperatures, the fire retardants are decomposed during compounding or during molding to cause foaming or corrode molding machines. Hence, problems still exist with regard to thermal stability.